SWCNT are single surface carbon nanotubes and for exploiting especially the electronic properties which vary with their chirality, you have to use only SWCNT.
MWCNT are multi-surface materials and would lose special electronic properties. They will show an average effect of all chiral tubes. Therefore use of these in mechanical and thermodynamical properties will be ok.
MWCNT are cheaper to produce, much cheaper compared to SWCNT. Therefore, they can be profitably used to make polymer or other composites enhancing their mechanical, thermal and electrical properties.