For example, the common restriction enzyme EcoRI recognizes the palindromic sequence GAATTC and cuts between the G and the A on both the top and bottom strands.
[2] Blunt ends are much less likely to be ligated by a DNA ligase because the blunt end doesn't have the overhanging base pair that the enzyme can recognize and match with a complementary pair.
In the case of the example the AATTG would have a complementary pair of TTAAC which would reduce the functionality of the DNA ligase enzyme.
Restriction sites are also important consideration to be aware of when designing plasmids.
[5][6] Recently, it has been shown that statistically significant nullomers (i.e. short absent motifs which are highly expected to exist) in virus genomes are restriction sites indicating that viruses have probably got rid of these motifs to facilitate invasion of bacterial hosts.