Echoing content is a very common task while using PHP. Using full stops to seperate strings can be a little slower than using commas.
Here is a quick example of the differences.

Joining two 100 characters strings four million times:

echo $string1, $string2;
Approx average 1.48 seconds

echo $string1 . $string2;
Approx average 1.62 seconds

print $string1 . $string2;
Approx average 1.67 seconds

Joining three 100 characters strings four million times:

echo $string1, $string2, $string3;
Approx average 2.08 seconds

echo $string1 . $string2 . $string3;
Approx average 3.48 seconds

print $string1 . $string2 . $string3;
Approx average 3.52 seconds

[ Examples from electrictoolbox ]

Using a full stop to concatenation the strings will mean PHP joins all the strings together before echoing them, while using commas will print them in turn.

It’s a subtle change, but can make a big difference if using a big data set such as a large CSV file and a handy thing to know if your PHP apps are a little unresponsive.