Attack is pretty decent for a monster that requires a 1 tribute.
It can destroy cards on your opponent's back row.
Defense is low which makes it susceptible to attacks when switched to defense position.
You have to send a face-up Continuous Spell Card from your field to the Graveyard in order to use its effect.
You might need the effect of the sent Continuous Spell card to the Graveyard later on.
Destroying opponents backrow
By using Magna-Slash Dragon's effect, you can send Dimension Gate to the Graveyard to destroy 1 card from your opponent's back row. It will trigger Dimension Gate's effect which is to Special Summon the monster that is banished by its effect.
Sends from field to Graveyard for cost / Sends from your field to your Graveyard
Destroys your opponent's Spell Cards / Destroys your opponent's Trap Cards