As others have said, the MXPL is definitely worth it for a variety of reasons... one not mentioned being that it's range bands overlap with SRM's and IS SSRM's.
I'd like to add in the SXPL, which is also quite a good weapon in it's own right... not only as a CQC damage dealer, but also as an anti-infantry weapon, since it has the same boni that all other small pulses have against infantry. The slightly higher heat is negligable compared to the much better range in that role.
IMHO, the only black sheep of the bunch is the LXPL. It's heat is just too much for what it brings to the table. It might be a good to back up for very low heat weapons like the Gauss Rifles, but compared to the other two XPL's it's simply too hot.
If you want a weapon with the same damage and range, for lower heat, with an inbuilt accuracy bonus(although a weaker one), I'd go for the LREL instead. Damage of the LPL/LXPL, range of the LL, lower heat than the regular LPL... 1 point more than the LL for 9 points and thus a 1-1 dmg-heat ratio, just like the LL(!!) and a -1 accuracy bonus, all for only a single ton more than either a LPL or LXPL. And as an added bonus, you get to laugh at reflective, Ferro-Lam and Hardened armor. Against Hardened Armor in particular, you effectively deal double damage! :thumbsup:
If we're comparing the LXPL and the LREL with an added TarComp, the LREL comes out ahead as well. Sure it's "only" -2 compared to -3 accuracy, but once you factor in the TarComp's weight and crit requirements, as well as the massive crit requirements of the DHS needed to get an LXPL heat neutral, that's almost not worth mentioning... it's a 2/3rds reduction compared to the 1/2 reduction without a TarComp.
The only real downside is the crit requirement... 5 critical slots compared to 2. That might be a problem on Mechs using lots of non engine mounted DHS, Endo/Ferro or other crit intensive weight savers or special armors.