Is it important to consider cable sizes during any installation?

Its a must for every project. Oversize cable is waste of money and under-size can cause short circuit or fire.

Also you have to consider the type of cable (single core , multi core) what ever is suitable for your application. Last but not least is the way you lay the cable. You must take into consideration that the cable is in a trunking or on cable trays.

Proper sizing of cabling is most important design feature in Electrical Engineering for the reliability, consistency and safety of the system.

Yes it is, in my opinion as per my experience are listed below..

1. To avoid reaching maximum allowable temperature of a certain size of cable.

2. To avoid heat-melting of cable.

3. In a certain size of conductor there are equivalent maximum current rating as per NEC to be follow for the safety of a installed electrical system and people.      

Yes Off Course..It depends upon Design and Load of the Project..

No. Not during installation. You must consider cable sizes as well as pipe sizes and so on... before installation and hint your client in the case of any difference between equipment's technical documents and executive drawings. It is common in projects when you find some clashes and must solve it before installation.  

Yes it is . Because wrong selection of cable can  burn your factory .

Yes there is a difference in the size of the cables by p voltage and current user and also by weather

yeah sure, you can't ignore that stuff, because it is basic thing

For Design sustainability, safety and cost optimization it is very important to size the cable as per the requirements.

yes it is,because depending on the current the conductor size will vary ,the larger the current the bigger the cables vice verca