Conventional lenders have guidelines about the property quality. They also lend based on purchase price. HMLs will lend on junky properties, and will base the value on the work you propose to do.
Hard money makes sense for buying junkers, fixing them up and then either selling them or refinancing into a conventional loan.
An example.
Property value fixed up (ARV): $100K
Purchase price: $55K
Rehab work: $15K
Conventional max LTV: 75%, based on purchase price
Max conventional loan: $37,875
Cash required: $31,125
HML max LTV: 70%, based on ARV
Max HML: $70,000
Cash needed: $0
Now, that's not exactly true because a HML will have steep points and interest, so you'll have to cover those as well as covering the closing and holding costs. So, realistically, you'll need about $10-11K to do this deal with hard money. You'll have points, closing costs, and holding costs on the conventional loan, too, about $4-5K total. So with a conventional loan you would need about $35K to do this deal, with hard money you can do it would about $10K.
Terms on hard money are typically 6-12 months. If you can't sell in 6-12 months, you'll be expected to quietly hand over the property.
Hard money is typically only for investment property, not for a property you're going to occupy.