I ran into issues when having lots of high-res raster assets-fans spun up like crazy and my machine slowed to halt but that was actually a really crazy edge-case (I converted a bunch of PDF files into JPGs to use as assets for a concept app and they averaged at ~3000x4000 each jpg for some reason.) It also froze up when using some of the raster-editing tools built into Sketch but I wouldn't recommend relying on those anyway. Sketch 3 worked great for small projects and I used the Marvel plugin pretty often.
Being a student and not knowing much about Apple computers at the time, I only opted for the base-level mid-2012, non-retina 13' MBP (2.5 i5, 4GB RAM, 500GB HDD) which I never upgraded in the 3 years I owned it and simply replaced with a mid-level 2015 15' MBP during my internship.
