Scanning large objects can be challenging because of:
The numerical limit of the software,
The maximum distance in one direction is 4m. the size limit is 8000*point-distance.
Therefore, you reduce the resolution to achieve singular large scan data
The cumulative error
The further you go the less accurate the data. Start from the middle of the object and follow a spider path towards the edges to reduce risk to of tracking loss.
If you misalign, recovering tracking can take long as there may be multiple possibilities of matching areas. The use of markers is highly recommended for large parts.
The computer capacity
The bigger the object, the larger the file. To improve this, register the GMF and construct the large file as a puzzle of smaller scans with a 3rd party software.