It's not the best starter 'Mech.
- Psychological Warfare: Small, narrow, fast and it flies high too. This 'Mech is the ultimate psychological warfare weapon in capable hands. For example, at the round start you can go for the enemy assaults slowly lumbering to join their team and keep them pinned. Most of them will struggle to even land shots on you (and will continue to forums to make a thread on how broken Spider hitboxes are), but the thing is even if you can't kill them you're essentially removing a significant chunk of firepower from the enemy frontlines. As long as you can keep enemies' valuable 'Mechs distracted by small pecks here and there, you're helping your team win the fight. Hilariously, sometimes a big chunk of enemy 'Mechs will break off from the frontlines to chase your tiny Spider, which is pretty much an autowin for your team. If you feel like things are going south, you always have boatloads of JJs to make your escape.
Not so perky stuff
- Assasin: A Spider is notoriously hard to kill and this makes them great assasin during stand-offs or full-blown brawls. You can wander inside an enemy group and take out that red ST Jager quickly, and get out without much damage.
- Firepower: As you noticed, the Spider's firepower is absymal. It takes a lot of time to kill fresh 'Mechs, so you're very dependent on your team to hurt enemy 'Mechs. You can solo enemy 'Mechs, but they either need to be terrible players, have terrible builds or just have a very slow 'Mech. The Anansi can actually solo fresh 'Mechs though.
Most of these stuff requires a very good knowledge of the enemy 'Mechs, weapons, the ability quickly assess enemy builds and player skills. That's why I said this isn't the best starter 'Mech. If you want to get in a Light and wreck faces immediately, go for a Jenner and Firestarter but bear in mind they also require a significant amount of experience to do well, but the Spider stands near the end of the spectrum.
- The leggening: Due to excessive JJ usage, the Spider takes a lot of leg damage and your enemies will actively try to leg you because your torso tanks so well. It really sucks.