Visa validity
The visa validity should be adequate to the travel purpose. On the visa sticker are mentioned: the dates of the validity of the visa, how many days the holder can stay in total on the territory of the Schengen States and the number of entries.

Examples:
Validity from 21.08. - 27.08, Duration of stay 07 days, Number of entries: 01
The holder of this visa is allowed to make a single journey between 21.08 – 27.08 and to stay up to 7 days on the territory of the Schengen States

Validity from 21.08. - 20.09 duration of stay 07 days, Number of entries: 01
The holder of this visa is allowed to make a single journey between 21.08. – 20.09 and to stay up to 7 days on the territory of the Schengen States

Travel dates unclear?
It happens that travels are planned but the exact period is not yet fixed or might be changed (especially business trips). In this case the Embassy suggests to the applicant to define a period in which the travel will take place (e.g. between 01.01 – 15.02) and also to define the number of days requested (e.g. 5 days). The applicant could get a visa which would be valid from 01.01. – 15.02 but only for 5 days. In this case the travel insurance has to cover 5 days during the period of 01.01 – 15.02! This solution is more evident than to ask for a 30 days business visa (to be sure not to miss the appointment) which often doesn't make sense in the context.

Single entry or multiple entry? Examples: 
one entry: a visa is valid from 01.01. – 15.01 and allows one entry. During that period the holder is allowed to travel once to the territory of the Member States; once he has left the territory of the Member States, he is not entitled to re-enter even if the total number of authorized days of stay have not been used. Applicant who travels for the first time to Switzerland/Liechtenstein/France will usually get a visa valid for a single entry.

two entries: a visa is valid from 01.01. – 30.06 and allows 2 entries with a total duration of stay of 15 days. During that period the holder may be authorized to stay for a total of 15 days divided into two separate trips. Two entries are generally granted if two business meetings are already set and confirmed. The insurance must cover both trips.

multiple entries: a visa is valid from 01.01.-31.12 and allows multiple entries. During this period the holder is allowed to stay up to 90 days per six-month period. The stay can be divided into as many separate trips as wished by the visa holder. Visas with multiple entries are only issued to bona fide applicants and granted with restraint.