Short answer- YES.
You may not notice it right away but eventually things will start to not display correctly and you will loose access to some tools or settings.
If you want to rum more than one session on your machine you need to make duplicate .upf and interface files.
Example- we have individual files for each user by initials. So when we start Mcrosation we only choose the Project. User and Interface are automatically selected base on Windows login. If I have one session open (using my User & Interface) and I want to open a new session, I open Microstation and choose another user and interface. I use my initials again but I usually preface that with an X so it is at the bottom of the list of users.
The problem with having more than one session open at a time is that the .upf file is being written to as you work so if you have 2 different sessions open the data gets "corrupted/confused"