I've never used the 'offset registration' commands more than once in a job (they are supposed to be job-level commands), so I can't (yet) confirm Jim's assertion that they can be used to dynamically shift the offset multiple times per line or page.
Just to make the sequences a bit clearer, here is an analysis of your first PCL snippet:
<Esc>E Printer Reset<Esc>&l2a Page Size: Letter
0o Orientation: Portrait
6d Line Spacing (6 lines-per-inch)
0e Top Margin (0 lines)
-216u Left (Long-Edge) Offset (-216 decipoints)
216u Left (Long-Edge) Offset (216 decipoints)
0z Top (Short-Edge) Offset (0 decipoints)
66F Text Length (66 lines)Note that I've replaced the final "f" with "F" to make the PCL conform to the specified syntax.
Note also that setting the left offset to two different values in succession (without any intervening data) doesn't really make any sense.
... and here is an analysis of the second PCL snippet:
<Esc>E Printer Reset<Esc>&a1L Left Margin (column 1)<Esc>&l-163U Left (Long-Edge) Offset (-163 decipoints)<Esc>&l0E Top Margin (0 lines)<Esc>&l0Z Top (Short-Edge) Offset (0 decipoints)<Esc>&l66F Text Length (66 lines)<Esc>&l7.38C Vertical Motion Index (7.38/48 inches)<Esc>(s10.5H Primary Font: Pitch (10.5 characters per inch)<Esc>&u6D Unit-of-Measure (6 PCL units per inch)<Esc>&l1H Paper Source: id 1 is Printer Dependent
Note that the font 'pitch' sequence is only relevant if the currently selected font is one of the (few) fixed-pitch fonts normally available on LaserJet printers (i.e. probably Courier or Letter Gothic).
... and the value associated with the unit of measure sequence is invalid (and will hence be ignored); the allowed values are 96, 100, 120, 144, 150, 160, 180, 200, 225, 240, 288, 300, 360, 400, 450, 480, 600, 720, 800, 900, 1200, 1440,1800, 2400, 3600, 7200, and the most commonly used value is 600.