He will read the lease and give you advice on the terms of the lease, its fairness, the conditions it imposes and the protections it offers to both you and the landlord.
If you then follow his advice he also takes on liability for the advice he gives you, this can be very useful. We leased a commercial property with what we thought was an option to buy, when we tried to exercise the option we had to pay £70,000 more that we had been led to believe. Our solicitor had read the lease wrong and as a consequence the advice he gave us was demonstrably wrong. His insurers paid out the £70k.
Had we had not of used him, we would have never spotted the faulty clause in the lease and would have been out of pocket.
For the level of protection it offers you it is worth using a specialist solicitor.