I have yet to be convinced of the nerfing of movement on a medium or the sizeable weight investment into a 2nd movement point on an assault.
For any suit, a DWP is generally worthwhile in construction terms if the mass you save is greater than the mass you spend on the 2nd MP. Technically that means it's always worthwhile for a quad, but you'd then want to consider the mobility loss. It can sometimes also be worthwhile even if inefficient in mass terms if you're struggling for slot space.
So for a bipedal assault, you need to install weaponry in DWPs that masses 640kg or more before the effects of the DWP for it to be worthwhile in terms of mass. Any medium-sized laser apart from the ML would thus be suitable, but for the ML or other lighter weapons you need more than one.
As for a medium, then only slot limits or flavor should indicate the use of a DWP. For example, if for some reason you really wanted an Anti-Mech capable suit that was equipped with Mimetic, a Magshot and a LRR, then you'd have to use a DWP on the Magshot, and possibly the LRR depending upon how much armor you wanted. I wouldn't want a suit like that, as the whole point of mediums is to be the mobile killers.