Think about the loos!
Think about the catering
Think about the clearing up
Think about the preparation.
Are they offering to pay for someone to come and cut your grass, tidy up the borders etc. before the wedding?
Are they offering to pay for portaloos to be installed?
Will they need to use your house for the catering?
Have they thought about a water supply?
Will they organise for all the mess to be cleared up?
How many people are they inviting?
How will your neighbours feel about the noise?
Will there be a band?
Will they be organising a generator?
Are people likely to get drunk and fall over in your flowerbeds (or worse!!!)
I think before you consider it, you need to know the answer to some of these questions.