The primary and immediate reason to cleanse yourself like this is, of course, to be able to stay grounded in the present in order to practice multidimensional exercises. If you have ties here and ties there, attachments here and attachments there, you won't be able to focus in the sense that you need to.
However, as I've hinted, there is a secondary reason as well, which is of no less importance. It is that of managing psychic attacks. I mentioned in the Wes Penre Papers that in a Pleiadian channeled session with an audience of 15 people (of evolved people), 11 of them had attachments, meaning spirits of some kind attached to them, according to the Pleiadians.
Some of them had more than one. In other words, this is extremely common. Not all of these spirits are malevolent, but some of them are. Those who are not, may be deceased relatives, generational spirits that go from family member to family member from generation to generation, or they can be attachments the person has had for hundreds of years, following the host even into the astral. Others are just lost spirits, who don't realize, they are dead and attach to anyone, who does not have enough boundaries.
Even if the entities are not evil, all of them, without exception, pull from your energy like vampires and can make you exhausted and lethargic for no obvious reason. Then there are more vicious attachments, such as hitchhikers, who are too lazy to take bodies of their own and instead want to run yours.
Others (and this is much more uncommon) could be a member of the AIF, who have decided to use your body for whatever purpose. This is quite unlikely, unless you are of a Global Elite bloodline in a relatively powerful position.
The first thing to do is not to run to an exorcist if you suspect you have attachments. Instead, you learn to set boundaries, and you started already by taking responsibility for your human connections (above). The next thing is to learn how to ground yourself - something of utmost importance!
Imagine a powerful pillar of light coming from the cosmos, hitting your Crown Chakra (the top of your head), and go right through your body and deep down into the Earth. At the end of this pillar of light, imagine yourself creating a big anchor, also made of light, and anchor yourself there, deep under the ground.
Then follow the light pillar backward (but always with the anchor well hooked into the Earth) until it reaches your feet. Then let the light form an egg-shaped halo around your body from your feet to the top of your head and close it there. Make this light bright and golden. Then let your spirit go over the egg-shaped golden orb all around you to make sure there are no holes in it anywhere.
If there is, seal them. If part of the orb is too close to the body (5-6 inches (15cm) away from the body is the best), let your spirit hands push it out until it is in the right position all the way around. Then put a cloak around you, if you want to be invisible to the spirit world. If not, skip this last step (it's mostly for people who are out there, like I am).
You are now shielded and have set up your boundaries. Beings who come from outside and see your shield will not even attempt to break through it. In addition, they can see you are anchored, so there is no way in, and if they had malevolent intentions, they will leave.
Imagine this pillar of light, the anchor, and the egg-shaped golden orb around you a few times a day to make sure you keep yourself protected. After a while, you only need to give it a quick thought, like pillar, and the whole image appears in your mind and you're protected.
I learned this way of shielding myself from the Pleiadians, but not from the same session where they mentioned the attachments, which is an older session. The session where they taught us how to shield ourselves is from February, 2013.
There are of course other ways you can protect yourself, and whatever works for you is good. This particular shield I just mentioned happens to work well for me. In my field of work, entities always try to enter and disturb and destroy, but after applying the above, it made a lot of difference.