It's a fair idea if you don't have enough resources for both a road and cross bike.
Assuming you don't race crits etc I don't think it would really affect you that much. Only thing to consider is that a cross frame used as a road frame is never quite as much fun on the road, and that there's a fair bit of difference between a more burly XC 29er and a crosser.
In terms of sizing you might have to size down a bit and run a bit of stack - or a flipped stem - for off road duties then swap to a longer stem for road, assuming the frame you went for is shorter and a bit more upright than the equivalent road frame.
It's a fair idea if you don't have enough resources for both a road and cross bike.
Assuming you don't race crits etc I don't think it would really affect you that much. Only thing to consider is that a cross frame used as a road frame is never quite as much fun on the road, and that there's a fair bit of difference between a more burly XC 29er and a crosser.
In terms of sizing you might have to size down a bit and run a bit of stack - or a flipped stem - for off road duties then swap to a longer stem for road, assuming the frame you went for is shorter and a bit more upright than the equivalent road frame.