On impossible it is not as easy and delays especially Tier 4 considerably which harbors the most important PSI Skills for pure PSI characters, Electron Supression which is the only efficient skill to deal with robots as is Photonic Redirection and of course Cerebro Extension which deals about twice more base damage than the wrench (7 vs 15) and can even one shot robots with Adrenaline.

In normal and standard it is no problem to get Hack 3 to hack replicators for cheap PSI Hypos and Hack 1 helps dealing with turrets and alarms early on.

Even though PSI is kinda underpowered compared to Hack/Standard I really like it especially Cerebro Extension with Invis and Adrenaline Overproduction but also Remote Hacking, Hypnogenesis, Electron Supression, Agility, etc. That being said, great page here and I have the following dilemma. I currently use the 'Newbie' Mod List since I prefer to keep the game close to the original albeit I did browse through some mods to look up what it's about but could not find a let's say subtle PSI mod which just slightly improves PSI. I just recently rebought the game on GoG since I enjoyed it back in the late 90s just as much as I enjoyed Deus Ex. I did beat the game twice, oce on normal and hard in some distant past. Just recently registered here and looking for some input.

System shock 2 impossible difficulty