I'd guess it's quite heavy flux residue.
It should not interfere with soldering or desoldering (it helps there in the first place), but it can interfere with the operation of the circuit. Especially if you try to build some low power / high impedance circuits...
Clean it with some ethanol or isopropanol.
Based on the comments it seems to be glue, so in that case:
It will interfere with soldering or desoldering. It will likely burn (or boil) and create some toxic fumes. It can also attack the tip of your iron and make it unusable because the tin won't wet it anymore (maybe you can clean the residues off, but if you are unlucky you need a new iron).
In this case you should definitely try to clean it off before doing soldering near that stuff. Hardened glue might need some special treatment to come off though. Some require heating (up to 150°C) and then you can wipe them off, others will come off with some solvent.