SF usually goes in the mid lane as a solo in order to get XP/farm and shut down his opponent using his lane dominance. Even if he doesn't dominate the lane, he is a flash farmer and can use his Razes to push out the creep wave and stack and farm the nearby jungle camps. Raze also has a very good kill potential. This means that with rotations from your supports it is possible to get kills on your lane opponent.
MAJOR
Damage Dealer: Virtually every skill of the hero revolves around dealing damage. One of your two passives increases the damage of your attacks, while the other reduces armor. Your four active skills give you incredible nuking potential. With your maxed ultimate you could theoretically deal more than 2k magical damage to a target in melee range, while the hitting all three Razes deals over 1k.
Strong Laning Presence: If you manage to steal some souls with Necromastery it will be relatively easy to dominate the last-hit war in the lane because of the high damage you deal with every hit. In addition, your Shadowraze is one of the best nukes for lane control – it allows you to easily take last hits, harass or push out the wave in seconds.
Flash Farmer: Shadowraze is one of the fastest and most cost-efficient spells for killing-off waves or camps. Using all three Razes is usually enough to kill even large camp stacks. With the use of this skill and the help of some mana sustain you are one of the fastest farmers in the early and mid game. Moreover, your high damage (Necromastery) and armor reduction (Presence) help you kill creeps at a fast pace even when you don’t have mana (or when your targets are magic immune).
MINOR
Armor Reduction: The armor reduction aura allows SF to have synergy with other physical damage dealers. It also makes him a viable part of armor reduction strategies.
AoE Presence: Thanks to his ultimate and partly to Shadowraze SF has AoE presence which makes him a good team fight carry. It is worth keeping in mind that his ultimate provides some useful utility - it slows and reduces the damage of all enemies caught in the AoE (which is very large).
Versatile Carry: SF is quite versatile especially in terms of item builds. This means that you can play him as a magical damage semi-carry or a typical physical damage carry. Either way, this versatility allows him to be useful in various strategies.